baddog1946 wrote:These guys have the new tubes for the best deal on the net I can find. $89.95 per pair. I just bought a quad for the same price as Genelex KT-88's.At that price why not?http://www.partsconnexion.com/

However don't you need to run them at like 100 milliamps to really make them worth having? And as I recall in another thread the current st 120 kit with the cap upgrades etc, doesn't really have enough power supply to push that kind of power through a quad of KT120's

RichJB603 wrote:However don't you need to run them at like 100 milliamps to really make them worth having? And as I recall in another thread the current st 120 kit with the cap upgrades etc, doesn't really have enough power supply to push that kind of power through a quad of KT120's

Hi Rich,

The KT120 tubes are capable of 120 - 140 watts from a PAIR of tubes IF you run 100 to 120 milliamps through each tube and get the B+ voltage up above 600 volts. I don't know of any present amplifier today that can take advantage of the full worth of these tubes and produce 120 watts or so from a PAIR of these tubes.

The ST-120 amp kit can run the KT120 tubes at 75 milliamps per tube (and maybe even higher) but the ST-120 amp runs a B+ voltage of about 500 volts - too low to produce what these tubes are capable of. They are usuable in the ST-120 but won't produce any more power than if you use a KT88 in the ST-120. In time someone *may* design an amp around these tubes with the proper parameters to get 120+ watts from a pair of these tubes. There is a danger, however, in designing such an amp for just ONE TYPE of tube from ONE MANUFACTURER. What if the tube prove to be unpopular and don't sell well? Tung-Sol may pull the plug on these tubes and you are stuck with an amp that uses extinct tubes?

Thats what I was thinking, while they might be fun to play with if you really can't get the full advantage out of them (due to not being able to supply enough current) it seems like a bit of a waste. Btw, and on another note, the ST 120 on the opening page of your website (courtesy of JJM) do you know what tubes he's running? They have a lot more 'blue' to their glow than others I have seen and I am just curious. I had some sylvania 6v6GT's that did that and supposedly the bendix's of the same type are well known for having a very blue'ish glow.

Those are a matched quad of Sovtek KT88 tubes. I can tell because Sovtek's have a stainless steel base and a slightly different "coke bottle" shape than other KT88's. If you turn out the lights in your music room at night and look closely, many brands of KT88 tubes will show a slight bluish glow in certain areas of the tube. Some have more blue than others ...

FYI: In some instances "blue glow" is not necessarily a good thing. It can be caused by the fluorescing of gasses in the tube. If memory serves me (a tenuous concept) "blue glow" is more serious if it originates in the area of the elements. Some blue glow near the surface of the glass envelope is not considered to be serious. Ex: for a number of years I had a single-ended amplifier in which I used some WWII vintage RCA 2A3 (JAN) tubes. These tubes would often produce some blue areas just inside the glass. I never noticed any ill effects from these.

I've heard this before that a 'gassy' tube will emit a 'blue' glow near the plates, but I was just referring to against the glass which as I understand it is the result of electrons reflecting off of it in some designs because of the distance between the plates and glass is more pronounced and not necessarily indicative of a problem.

I have been running the gold lion KT88's and they aren't very blue, but I am running them pretty much dead on @ .550v I am sure I could bias them up a little more (perhaps .560-.570) without much ill effect but I have noticed some tubes 'have it' and some others just don't. I haven't noticed any relation between sonic fidelity and color of the glow, it's just the blue makes for nice aesthetics. The sylvania 6v6's I used to run in my old ST70 had a lot of blue to them and sounded great IMO. As much as I like that color I am not the type to sacrifice clarity or tonal quality for an aesthetic quality.